The exemplary embodiment relates to a controlled release material for delivering small molecules into an aquatic environment. It finds particular application in connection with a composite material in which a micellized anti-foulant compound or composition is held within pores of a mesoporous or microporous oxide structure by a surfactant.
In aquatic environments, such as seawater or freshwater in lakes and rivers, biofouling of ships and other structures by biofilms made up of bacteria, algae, seaweed and the like as well as attachment of larger organisms such as barnacles, mussels, and tubeworms, can cause a variety of problems. Such biofoulants on a ship's hull can add considerably to the drag, which increases fuel consumption and green house gas emissions, and can also result in corrosion.
Antifouling paints and coatings have been developed to reduce buildup of biofoulants. A number of the marine antifoulant approaches are environmentally unsuitable since they use antifoulants that are considered pollutants. Several new approaches include controlled release of a nonpolluting agent specific to particular fouling organisms or to its adhesive chemistry and release of an agent that keeps renewing a non-adhesive surface, e.g., silicone, which may slough off continuously.
Biofouling of underwater sensors which rely on transmission of light is also a problem. Ocean bottom sensor nodes and Unmanned or Autonomous Underwater Vehicles (UUVs, AUVs), for example, may be equipped with sensors, and can be used for tactical surveillance applications and in situ long term monitoring for oceanographic data collection, pollution monitoring, and offshore exploration. However, deploying such a sensor in seawater or subsurface environments for extended periods of time exposes it to chemical and microbial degradation. Underwater sensors are thus prone to failures because of fouling, corrosion, and the like, and even the most advanced sensor systems may be rendered useless in a short period of time, such as a few weeks. Frequent, labor intensive and expensive maintenance may be required to maintain such sensors operational. Current antifouling coatings may not provide sufficient antifouling protection or may interfere with a signal being sent and/or received by the sensor.
It is known to use mesoporous silica materials for slow release of drugs, such as ibuprofen and amoxicillin. See, for example, Vallet-Regi, et al., Chem. Mater. 13 (2): 308-311 (2001) and Vallet-Regi, et al., Sol. State Ionics 172 (1-4): 435-439 (2004). The release rates from the silica are fairly rapid, on the order of hours. Methods have been developed to slow the release rates, e.g., with a coumarin derivative grafted to pore openings (see, Mal, et al. Nature, 421, 350-353 (2003); and Mal, et al., Chem. Mater. 15 (17): 3385-3394, (2003)), or with other reversible plugging agents (see, e.g., Nguyen, et al., Proc. Nat. Acad. Sci. USA 102 (29): 10029-10034 (2005); and Lai, et al., J. Am. Chem. Soc. 125 (15): 4451-4459 (2003)). However, even with such complex release mechanisms, in all cases, release is largely complete after 96 hours or less.
Existing materials also tend to degrade very rapidly in seawater.
There remains a need for improved methods and systems for controlled release of antifoulants and other small molecules which are suited to marine environments.